Industrial computed tomography (CT) scanning systems can be commonly used to produce three-dimensional representations of industrial parts. For example, industrial CT scanning systems can facilitate nondestructive internal inspection of industrial machine parts. As a result, CT scanning can be used for flaw detection, assembly analysis, and failure analysis of machine parts. CT scanning involves irradiating a machine part with an electromagnetic radiation (e.g., X-ray) and detecting a portion of the radiation that is modified (e.g., transmitted, reflected, and the like) by the machine part. This process is repeated for various orientations of the machine part and at various locations of the machine part with respect to the source of the radiation. Based on detection of multiple images of the machine parts (e.g., for the various orientations and locations), a three-dimensional representation of the machine part can be generated (e.g., by a computing device).
CT scanning systems have to be calibrated (e.g., prior to a measurement) for generating accurate three-dimensional representations. System calibration can involve assessment of dimensional measurement capabilities and measurement uncertainty (e.g., length measurement errors) of the scanning system. This can be done by scanning a measurement phantom having known physical properties (e.g., shape, size, material composition, and the like) and calculating measurement uncertainty based on the generated-three dimensional representation and the known geometry of the phantom.
Guidelines such as VDI/VDE 2630-1.3 and ISO draft 10360-11 provide guidelines for specifying the accuracy of x-ray CT scanning systems. For example, according to VDI 2630 guidelines, length measurements of the phantom are performed in three directions (e.g., horizontal, diagonal and vertical), and in each direction there are at least five preferably evenly distributed distances. Further, according to the VDI 2630 guidelines, length measurements of the phantom should be performed at two locations (e.g., resulting in two magnification) and the longest length measurement should be at least 66% of the length of a scan volume. CT system operators can verify whether the CT system reaches the specified accuracy with a process and a phantom satisfying the VDI/VDE 2630-1.3 and ISO draft 10360-11 guidelines.
The phantom used in the calibration of CT scanning systems can facilitate the length measurements described in the VDI 2630 guidelines. For example, the phantom can include geometric markers that allow for the prescribed length measurements. A commonly used phantom is a ball bar that includes a bar that can rotate about an axis and to which several balls are rigidly attached. In order to satisfy the requirements of the VDI 2630 guidelines, the ball bar is placed at two locations (e.g., with respect to the X-ray source of the CT scan system), and at each location, the orientation of the bar is altered. For example, the bar needs to be oriented along a vertical direction, a horizontal direction and a diagonal direction at each of the two locations. This can be done by manually varying the orientation of the bar. However, adjusting the ball bar by hand during the calibration process can introduce errors in the calibration and can slow the calibration process.